Received for publication October 16, 2007.
Revised December 20, 2007.
Accepted for publication December 20, 2007.

OSU-03012 stimulates PERK-dependent increases in HSP70 expression, attenuating its lethal actions in transformed cells

Abstract

We have further defined mechanism(s) by which OSU-03012 (OSU), a derivative of the COX2 inhibitor Celecoxib but lacking COX2 inhibitory activity, kills transformed cells. In cells lacking expression of PKR-like endoplasmic reticulum kinase (PERK -/-) the lethality of OSU was attenuated. OSU enhanced the expression of Beclin 1 and ATG5 and cleavage of pro-caspase 4 in a PERK-dependent fashion and promoted the Beclin 1- and ATG5-dependent formation of vacuoles containing LC3, followed by a subsequent caspase 4-dependent cleavage of cathepsin B and a cathepsin B-dependent formation of low pH intracellular vesicles; cathepsin B was activated and released into the cytosol and genetic suppression of caspase 4, cathepsin B or AIF function significantly suppressed cell killing. In parallel, OSU caused PERK-dependent increases in HSP70 expression and decreases in HSP90 and Grp78/BiP expression. Changes in HSP70 expression were post-transcriptional. Knock down or small molecule inhibition of HSP70 expression enhanced OSU toxicity and over-expression of HSP70 suppressed OSU-induced low pH vesicle formation and lethality. Our data demonstrate that OSU-03012 causes cell killing that is dependent on PERK-induced activation of multiple toxic proteases. OSU-03012 also increased expression of HSP70 in a PERK-dependent fashion, arguing that OSU-03012-induced PERK signaling promotes both cell survival and cell death processes.

Key words: MAP Kinase, Mechanisms of cell killing/apoptosis

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